In the printing, paper making and paint industries, the environmental problem of the recent concern has forced a transition to aqueous systems. As compared with the solvent system, the aqueous system is slow in drying rate and thus low in production speed. For acceptable productivity, a need to speed up the process is perpetually imposed on the aqueous system. It is required to improve ink properties so as to accommodate high-speed printing and high-speed coating.
Under the circumstances, the aqueous ink industry seeks for surfactants having a capability of reducing surface tension for imparting wetting, penetrating and dispersing properties relative to a substrate. The key for a choice of a suitable surfactant is a low static surface tension when the system remains static and a low dynamic surface tension during high-speed operation because of a need to speed up the printing process for higher productivity.
Acetylene glycol surfactants such as acetylene glycol and ethylene oxide derivatives thereof have a good balance of static and dynamic surface tension reducing capabilities, eliminate most drawbacks of prior art nonionic and anionic surfactants and have an antifoaming ability. They have been used as wetting and dispersing agents in ink and paint compositions.
However, the acetylene glycol surfactants have drawbacks including a low solubility in water and solidity at normal temperature. They are thus used in combination with solubilizing agents such as polyethylene glycol and polyoxyethylene nonylphenyl ether for imparting a self-emulsifying ability when added to aqueous ink compositions.
Polyoxyethylene nonylphenyl ether used as the solubilizing agent will encounter more strict legal control because the environmental problem of the recent concern draws attention to the TRI list substances and environmental hormone-containing substances. Under the situation, there is an increasing demand for surfactants which are compliant with the environment, and alternatives have been made by manufacturers.
Some of these alternative solubilizing agents, however, have an increased dynamic surface tension and contact angle. When a combination of acetylene glycol and an alternative solubilizing agent is used in ink, the ink gives rise to problems like cissing, bleeding due to deteriorated absorptivity, and varying spreads of ink on paper depending on the type of paper (or substrate to be printed). This brings about a substantial variation of print quality. The alternatives still fail to provide a measure sufficient to produce versatile color records of quality.
Known patents include JP-A 6-24006 and JP-A 2000-290549.